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Early detection and treatment of myocardial ischaemia after operation using continual ambulatory arterial pressure monitoring and ECG ST segment analysis
British Journal of Anaesthesia 1995; 75: 491–494
CASE REPORTS
Early detection and treatment of myocardial ischaemia after operation using continual ambulatory arterial pressure monitoring and ECG ST segment analysis N. D. EDWARDS, G. TROY, W. YEO, P. JACKSON AND C. S. REILLY
Summary We report a case in which the use of continual ambulatory arterial pressure monitoring and ECG ST-segment analysis allowed early detection and treatment of myocardial ischaemia in the postoperative period. We believe that this case illustrates the potential value of ambulatory monitoring in the early postoperative period in high-risk patients. (Br. J. Anaesth. 1995; 75: 491–494) Key words Heart, ischaemia. Monitoring, arterial pressure. Monitoring, electrocardiography.
The development of myocardial ischaemia in the early postoperative period is associated with adverse outcome [1, 2]. This ischaemia is usually silent and difficult to detect clinically [1]. We report a case in which the use of continual ambulatory arterial pressure monitoring and ECG ST-segment analysis allowed early detection and treatment of myocardial ischaemia in the postoperative period.
Case report A 60-yr-old female with known phaeochromocytoma was admitted for abdominal hysterectomy and bilateral odphorectomy for ovarian carcinoma, followed by bilateral adrenalectomy. She had angina, and had suffered a myocardial infarction 9 months previously. She also had neurofibromatosis, and had been epileptic for 30 yr. Her current medication consisted of phenoxybenzamine 10 mg b.i.d., atenolol 50 mg once daily, isosorbide mononitrate 60 mg once daily, aspirin 300 mg once daily, glyceryl trinitrate (GTN) as required, phenytoin 25 mg t.i.d., carbamazepine 400 mg b.i.d. and vigabatrin 1 g b.i.d. Her preoperative ECG showed Q waves in the inferior leads. The patient was enrolled into a study of perioperative myocardial ischaemia. The evening before surgery, ambulatory ECG monitoring of myocardial ischaemia and ambulatory arterial pressure monitoring were commenced. Ambulatory ECG monitoring was undertaken with leads II and CS5, using the Compas ambulatory ECG surveillance system [3]. Myocardial ischaemia was defined as STsegment depression of greater than 1 mm or elevation
of greater than 2 mm. Ambulatory arterial pressure monitoring was undertaken with a Spacelabs 90207 ambulatory arterial pressure monitor, which consists of a cuff and lightweight recorder, and has been recommended for ambulatory pressure measurement [4]. The monitor was programmed to record arterial pressure every 20 min from 07:00 to 22:00 and every 60 min overnight from 22:00 to 07:00. All medication was continued up to the morning of operation, and the patient received temazepam 20 mg orally as premedication 1 h before surgery. In the anaesthetic room, i.v. and intra-arterial cannulae were inserted under local anaesthesia, and anaesthesia was induced with fentanyl 200 g and thiopentone 175 mg. Neuromuscular block was produced with vecuronium 8 mg and tracheal intubation performed. The patient’s lungs were ventilated with isoflurane and nitrous oxide in oxygen. Neuromuscular block was maintained with bolus doses of vecuronium. Ambulatory ECG monitoring was continued throughout the operation. At operation hysterectomy and bilateral oophorectomy were performed, but metastatic seedings were found. Following discussion between gynaecological, general surgical, anaesthetic and medical teams, it was decided not to proceed with adrenalectomy, but to continue to treat her phaeochromocytoma medically, and to reconsider adrenalectomy at a later stage depending on her response to chemotherapy. Neuromuscular block was antagonized with neostigmine 2.5 mg and glycopyrronium 0.5 mg. The intra-arterial cannula was removed in the recovery room. After operation the patient was nursed on a general ward. Oxygen was prescribed for the first 24 h and analgesia was provided with morphine via a patient-controlled system. The ambulatory ECG and arterial pressure monitors are able to store 24 h of data, following which they are downloaded to a designated printer. The monitors were downloaded after surgery and then recommenced while the patient was still in the recovery room. Both ambulatory ECG and arterial pressure monitoring were continued for 3 days after
N. D. EDWARDS, FRCA, G. TROY, BA(HONS), RGN, C. S. REILLY, MD, FRCA (University Department of Surgical and Anaesthetic Sciences); W. YEO, MRCP, P. JACKSON, FRCP (University Department of Medicine and Therapeutics); Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF. Accepted for publication: April 28, 1995.
492
British Journal of Anaesthesia
Table 1 Perioperative heart rate (HR) and mean arterial pressure (MAP) (mean (range))
Preoperative Postoperative Day 1 Day 2 Day 3
HR (beat min⫺1)
MAP (mm Hg)
66.6 (59–72)
83.4 (74–97)
97.4 (64–114) 98.5 (82–124) 104.7 (84–117)
103.0 (96–115) 94.2 (77–115) 98.9 (85–119)
Figure 1 Mean haemodynamic variables (heart rate (HR) and mean arterial pressure (MAP)) each hour before operation. Figure 3 Mean haemodynamic variables (heart rate (HR) and mean arterial pressure (MAP)), ischaemic time and maximum ST-depression each hour during the second day after operation.
Figure 2 Mean haemodynamic variables (heart rate (HR) and mean arterial pressure (MAP)), ischaemic time and maximum ST-depression each hour during the first day after operation.
operation. Before operation the patient’s heart rate (mean 67; range 59–72 beat min⫺ 1) and arterial pressure (mean arterial pressure (MAP) 83; range 74–97 mm Hg) were well controlled (table 1, fig. 1), and the patient showed no signs of myocardial ischaemia. The following day, the monitors were downloaded again and showed that over the first few hours after operation, the patient had developed a
tachycardia which had become persistent at about 100 beat min⫺ 1. The patient’s arterial pressure control was also considerably worse than before operation (mean MAP 97; range 96–115 mm Hg). In addition, the patient had developed significant amounts of ST-segment depression commencing approximately 4 h after operation and becoming virtually continuous (fig. 2). These changes had occurred despite the patient receiving her regular hypertensive medication after operation. However, the patient had appeared well throughout this time, and had experienced no cardiac symptoms. Because of these ambulatory ECG findings, a 12lead ECG was performed which confirmed STsegment depression in leads V2 to V6. The medical team were contacted to review her treatment in the light of the myocardial ischaemia. The patient was given another 50 mg of atenolol orally, and the daily atenolol dose was increased to 100 mg. In addition, the patient was prescribed oral nifedipine 10 mg b.i.d. and oxygen therapy was continued for a further 24 h. Ambulatory monitoring was continued during the second postoperative day, and that evening, the patient began to develop angina, which was treated with GTN paste (1 inch q.i.d.). Ambulatory monitoring revealed that the patient’s heart rate and arterial pressure control had initially improved, but by the evening of the second postoperative day there had again been an increase in both heart rate and MAP. This was associated with further episodes of ST-segment depression on ambulatory monitoring, which had shown an increase in both duration and severity, and had led to her anginal symptoms, with ST-segment depression of greater than 4 mm (fig. 3). By the third postoperative day, the patient’s
Detection and treatment of myocardial ischaemia
Figure 4 Mean haemodynamic variables (heart rate (HR) and mean arterial pressure (MAP)), ischaemic time and maximum ST-depression each hour during the third day after operation.
angina had settled. Ambulatory monitoring showed that there had been little improvement in either heart rate or arterial pressure control, and the patient continued to show large amounts of silent myocardial ischaemia (fig. 4). However, there had been a reduction in the severity of myocardial ischaemia, and ambulatory monitoring was discontinued after the third postoperative day. A 12-lead ECG and cardiac enzyme analysis on the first 3 days after operation showed no evidence of myocardial infarction. Over the following few days the improvement in the patient’s cardiac symptoms continued. The patient exhibited no further attacks of angina, and the GTN paste was discontinued after 4 days. However, the patient continued to have problems with vomiting, diarrhoea and other complications relating to surgery, resulting in her discharge being delayed until 22 days after operation. The accumulated ambulatory data were analysed retrospectively. Over the total monitoring period, there was a significant positive correlation between the amount of myocardial ischaemia occurring during each 1-h period and mean heart rate (P ⬍ 0.001) and mean MAP (P ⫽ 0.032) during that hour. There was also a significant positive correlation between the maximum level of ischaemia seen during each hourly period and mean heart rate (P ⬍ 0.001) and mean MAP (P ⫽ 0.004) during that hour.
Discussion Myocardial ischaemia developing in the early postoperative period after non-cardiac surgery is associated with an increased risk of adverse cardiac events after operation [1, 2]. It therefore seems
493 reasonable to suggest that early treatment of myocardial ischaemia which may occur in the postoperative period would reduce the risk of such events. However, most episodes of myocardial ischaemia which occur in the postoperative period are silent [1], and therefore very unlikely to be detected routinely. In order that episodes of myocardial ischaemia are treated promptly, early recognition of silent myocardial ischaemia is essential. This can be achieved by continuous ST-segment analysis of the ECG [5]. The potential value of continuous ST-segment analysis after operation has been illustrated in two previous case reports. Clements, McCann and Levin [6] studied a patient who had undergone aortic aneurysm resection with postoperative ambulatory ECG monitoring of a bipolar, modified V5 lead. In addition, ECG lead II was being monitored continuously on the ITU. On the third postoperative day, the patient developed ventricular fibrillation from which he was resuscitated successfully. It was confirmed later that the patient had suffered an anterior myocardial infarction. Before this event, staff had not detected any ST-segment abnormalities on the bedside monitor, although increased ventricular extrasystoles had been treated with potassium. Analysis of the ambulatory ECG revealed that a trend was present in which there was a crescendo of abnormalities characterized by increased frequency of ventricular ectopic activity and ST-segment depression before the myocardial infarction and cardiac arrest. The authors proposed that had the information recorded by the ambulatory monitor been available to the attending staff, earlier treatment may have prevented cardiac arrest. Dodds and colleagues [7] reported a case in which a real time ambulatory ECG Holter monitor which was programmed to alarm when ischaemia was detected was used in a patient undergoing carotid artery surgery. In this case, detection of myocardial ischaemia occurred earlier, and consequently was treated earlier than would otherwise have been possible. Despite this the ischaemic episode progressed to myocardial infarction. However, the authors believed that relatively early recognition and treatment may have prevented further complications. Our patient was a high-risk cardiac case, with known phaeochromocytoma and previous myocardial infarction. The patient Was monitored with ambulatory arterial pressure monitoring and an ambulatory ECG monitor which was not programmed to alarm, but which requires downloading every 24 h. As a consequence, ST-segment depression indicating myocardial ischaemia was detected earlier than would otherwise have been the case. The additional use of ambulatory arterial pressure monitoring allowed us to observe that the development of myocardial ischaemia was associated with an increase in heart rate and arterial pressure compared with before operation when the patient had exhibited no signs of myocardial ischaemia. A 12-lead ECG was performed which confirmed the presence of ST-segment changes and the patient’s medication was altered in an effort to improve
494 haemodynamic control and reduce myocardial ischaemia, with an increase in atenolol dose and the commencement of oral nifedipine. Furthermore, staff were alerted to the patient’s condition. Despite this, the patient’s condition worsened and she developed symptoms of angina which required further medical treatment with GTN paste. However, the eventual outcome was good, and the patient did not progress to myocardial infarction. Several points are worthy of further comment. First, there are no previous reports of the use of ambulatory arterial pressure monitoring in the perioperative period. In this patient, we were able to identify that there was poor arterial pressure control after operation compared with before operation (using pressure recordings taken by the same monitor for a similar period), which in combination with an increased heart rate had resulted in myocardial ischaemia. Second, probably because the patient was initially asymptomatic, initial treatment was to increase the oral dose of -blocker and start a low oral dose of calcium antagonist. Had treatment been more aggressive at this stage, particularly with regard to improving heart rate and arterial pressure control with i.v. -block or GTN, myocardial ischaemia may have been controlled earlier, the development of angina prevented and the risk of progression to myocardial infarction further reduced. Indeed, even on the third postoperative day, heart rate and arterial pressure remained poorly controlled, and despite additional nitrate therapy, the patient continued to exhibit silent myocardial ischaemia. It was interesting that retrospective analysis of the data showed a significant association between heart rate and mean arterial pressure, and
British Journal of Anaesthesia both the duration and severity of myocardial ischaemia. Third, the monitors we use sound an alarm when ischaemia is detected, but for the purpose of our research this was disabled. Had the alarm facility been used, then myocardial ischaemia would have been detected at an earlier time.
Acknowledgement G. Troy is supported by a grant from Trent Health.
References 1. Mangano DT, Browner WS, Hollenberg M, London MJ, Tubau JF, Tateo IM. Association of perioperative myocardial ischaemia with cardiac morbidity and mortality in men undergoing noncardiac surgery. New England Journal of Medicine 1990; 323: 1781–1788. 2. Landesberg G, Luria MH, Cotev S, Eidelman LA, Anner H, Mossere M, Schechter D, Assaf J, Erel J, Berlatzky Y. Importance of long-duration postoperative ST-segment depression in cardiac morbidity after vascular surgery. Lancet 1993; 341: 715–719. 3. McHugh P, Gill NP, Wyld R, Nimmo WS, Reilly CS. Continuous ambulatory ECG monitoring in the perioperative period: Relationship of preoperative status and outcome. British Journal of Anaesthesia 1991; 66: 285–291. 4. O’Brien E, Mee F, Atkins N, O’Malley K. Accuracy of the Spacelabs 902207 determined by the British Hypertension Society protocol. Journal of Hypertension 1991; 9: 573–574. 5. Edwards ND, Reilly CS. Detection of perioperative myocardial ischaemia. British Journal of Anaesthesia 1994; 72: 104–115. 6. Clements FM, McCann RL, Levin RI. Continuous ST segment analysis for the detection of perioperative myocardial ischaemia. Critical Care Medicine 1986; 16: 710–711. 7. Dodds TM, Delphin E, Stone JG, Gal SG, Coromilas J. Detection of perioperative myocardial ischemia using Holter monitoring with real-time ST segment analysis. Anesthesia and Analgesia 1988; 67: 890–893.
CASE REPORTS
Early detection and treatment of myocardial ischaemia after operation using continual ambulatory arterial pressure monitoring and ECG ST segment analysis N. D. EDWARDS, G. TROY, W. YEO, P. JACKSON AND C. S. REILLY
Summary We report a case in which the use of continual ambulatory arterial pressure monitoring and ECG ST-segment analysis allowed early detection and treatment of myocardial ischaemia in the postoperative period. We believe that this case illustrates the potential value of ambulatory monitoring in the early postoperative period in high-risk patients. (Br. J. Anaesth. 1995; 75: 491–494) Key words Heart, ischaemia. Monitoring, arterial pressure. Monitoring, electrocardiography.
The development of myocardial ischaemia in the early postoperative period is associated with adverse outcome [1, 2]. This ischaemia is usually silent and difficult to detect clinically [1]. We report a case in which the use of continual ambulatory arterial pressure monitoring and ECG ST-segment analysis allowed early detection and treatment of myocardial ischaemia in the postoperative period.
Case report A 60-yr-old female with known phaeochromocytoma was admitted for abdominal hysterectomy and bilateral odphorectomy for ovarian carcinoma, followed by bilateral adrenalectomy. She had angina, and had suffered a myocardial infarction 9 months previously. She also had neurofibromatosis, and had been epileptic for 30 yr. Her current medication consisted of phenoxybenzamine 10 mg b.i.d., atenolol 50 mg once daily, isosorbide mononitrate 60 mg once daily, aspirin 300 mg once daily, glyceryl trinitrate (GTN) as required, phenytoin 25 mg t.i.d., carbamazepine 400 mg b.i.d. and vigabatrin 1 g b.i.d. Her preoperative ECG showed Q waves in the inferior leads. The patient was enrolled into a study of perioperative myocardial ischaemia. The evening before surgery, ambulatory ECG monitoring of myocardial ischaemia and ambulatory arterial pressure monitoring were commenced. Ambulatory ECG monitoring was undertaken with leads II and CS5, using the Compas ambulatory ECG surveillance system [3]. Myocardial ischaemia was defined as STsegment depression of greater than 1 mm or elevation
of greater than 2 mm. Ambulatory arterial pressure monitoring was undertaken with a Spacelabs 90207 ambulatory arterial pressure monitor, which consists of a cuff and lightweight recorder, and has been recommended for ambulatory pressure measurement [4]. The monitor was programmed to record arterial pressure every 20 min from 07:00 to 22:00 and every 60 min overnight from 22:00 to 07:00. All medication was continued up to the morning of operation, and the patient received temazepam 20 mg orally as premedication 1 h before surgery. In the anaesthetic room, i.v. and intra-arterial cannulae were inserted under local anaesthesia, and anaesthesia was induced with fentanyl 200 g and thiopentone 175 mg. Neuromuscular block was produced with vecuronium 8 mg and tracheal intubation performed. The patient’s lungs were ventilated with isoflurane and nitrous oxide in oxygen. Neuromuscular block was maintained with bolus doses of vecuronium. Ambulatory ECG monitoring was continued throughout the operation. At operation hysterectomy and bilateral oophorectomy were performed, but metastatic seedings were found. Following discussion between gynaecological, general surgical, anaesthetic and medical teams, it was decided not to proceed with adrenalectomy, but to continue to treat her phaeochromocytoma medically, and to reconsider adrenalectomy at a later stage depending on her response to chemotherapy. Neuromuscular block was antagonized with neostigmine 2.5 mg and glycopyrronium 0.5 mg. The intra-arterial cannula was removed in the recovery room. After operation the patient was nursed on a general ward. Oxygen was prescribed for the first 24 h and analgesia was provided with morphine via a patient-controlled system. The ambulatory ECG and arterial pressure monitors are able to store 24 h of data, following which they are downloaded to a designated printer. The monitors were downloaded after surgery and then recommenced while the patient was still in the recovery room. Both ambulatory ECG and arterial pressure monitoring were continued for 3 days after
N. D. EDWARDS, FRCA, G. TROY, BA(HONS), RGN, C. S. REILLY, MD, FRCA (University Department of Surgical and Anaesthetic Sciences); W. YEO, MRCP, P. JACKSON, FRCP (University Department of Medicine and Therapeutics); Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF. Accepted for publication: April 28, 1995.
492
British Journal of Anaesthesia
Table 1 Perioperative heart rate (HR) and mean arterial pressure (MAP) (mean (range))
Preoperative Postoperative Day 1 Day 2 Day 3
HR (beat min⫺1)
MAP (mm Hg)
66.6 (59–72)
83.4 (74–97)
97.4 (64–114) 98.5 (82–124) 104.7 (84–117)
103.0 (96–115) 94.2 (77–115) 98.9 (85–119)
Figure 1 Mean haemodynamic variables (heart rate (HR) and mean arterial pressure (MAP)) each hour before operation. Figure 3 Mean haemodynamic variables (heart rate (HR) and mean arterial pressure (MAP)), ischaemic time and maximum ST-depression each hour during the second day after operation.
Figure 2 Mean haemodynamic variables (heart rate (HR) and mean arterial pressure (MAP)), ischaemic time and maximum ST-depression each hour during the first day after operation.
operation. Before operation the patient’s heart rate (mean 67; range 59–72 beat min⫺ 1) and arterial pressure (mean arterial pressure (MAP) 83; range 74–97 mm Hg) were well controlled (table 1, fig. 1), and the patient showed no signs of myocardial ischaemia. The following day, the monitors were downloaded again and showed that over the first few hours after operation, the patient had developed a
tachycardia which had become persistent at about 100 beat min⫺ 1. The patient’s arterial pressure control was also considerably worse than before operation (mean MAP 97; range 96–115 mm Hg). In addition, the patient had developed significant amounts of ST-segment depression commencing approximately 4 h after operation and becoming virtually continuous (fig. 2). These changes had occurred despite the patient receiving her regular hypertensive medication after operation. However, the patient had appeared well throughout this time, and had experienced no cardiac symptoms. Because of these ambulatory ECG findings, a 12lead ECG was performed which confirmed STsegment depression in leads V2 to V6. The medical team were contacted to review her treatment in the light of the myocardial ischaemia. The patient was given another 50 mg of atenolol orally, and the daily atenolol dose was increased to 100 mg. In addition, the patient was prescribed oral nifedipine 10 mg b.i.d. and oxygen therapy was continued for a further 24 h. Ambulatory monitoring was continued during the second postoperative day, and that evening, the patient began to develop angina, which was treated with GTN paste (1 inch q.i.d.). Ambulatory monitoring revealed that the patient’s heart rate and arterial pressure control had initially improved, but by the evening of the second postoperative day there had again been an increase in both heart rate and MAP. This was associated with further episodes of ST-segment depression on ambulatory monitoring, which had shown an increase in both duration and severity, and had led to her anginal symptoms, with ST-segment depression of greater than 4 mm (fig. 3). By the third postoperative day, the patient’s
Detection and treatment of myocardial ischaemia
Figure 4 Mean haemodynamic variables (heart rate (HR) and mean arterial pressure (MAP)), ischaemic time and maximum ST-depression each hour during the third day after operation.
angina had settled. Ambulatory monitoring showed that there had been little improvement in either heart rate or arterial pressure control, and the patient continued to show large amounts of silent myocardial ischaemia (fig. 4). However, there had been a reduction in the severity of myocardial ischaemia, and ambulatory monitoring was discontinued after the third postoperative day. A 12-lead ECG and cardiac enzyme analysis on the first 3 days after operation showed no evidence of myocardial infarction. Over the following few days the improvement in the patient’s cardiac symptoms continued. The patient exhibited no further attacks of angina, and the GTN paste was discontinued after 4 days. However, the patient continued to have problems with vomiting, diarrhoea and other complications relating to surgery, resulting in her discharge being delayed until 22 days after operation. The accumulated ambulatory data were analysed retrospectively. Over the total monitoring period, there was a significant positive correlation between the amount of myocardial ischaemia occurring during each 1-h period and mean heart rate (P ⬍ 0.001) and mean MAP (P ⫽ 0.032) during that hour. There was also a significant positive correlation between the maximum level of ischaemia seen during each hourly period and mean heart rate (P ⬍ 0.001) and mean MAP (P ⫽ 0.004) during that hour.
Discussion Myocardial ischaemia developing in the early postoperative period after non-cardiac surgery is associated with an increased risk of adverse cardiac events after operation [1, 2]. It therefore seems
493 reasonable to suggest that early treatment of myocardial ischaemia which may occur in the postoperative period would reduce the risk of such events. However, most episodes of myocardial ischaemia which occur in the postoperative period are silent [1], and therefore very unlikely to be detected routinely. In order that episodes of myocardial ischaemia are treated promptly, early recognition of silent myocardial ischaemia is essential. This can be achieved by continuous ST-segment analysis of the ECG [5]. The potential value of continuous ST-segment analysis after operation has been illustrated in two previous case reports. Clements, McCann and Levin [6] studied a patient who had undergone aortic aneurysm resection with postoperative ambulatory ECG monitoring of a bipolar, modified V5 lead. In addition, ECG lead II was being monitored continuously on the ITU. On the third postoperative day, the patient developed ventricular fibrillation from which he was resuscitated successfully. It was confirmed later that the patient had suffered an anterior myocardial infarction. Before this event, staff had not detected any ST-segment abnormalities on the bedside monitor, although increased ventricular extrasystoles had been treated with potassium. Analysis of the ambulatory ECG revealed that a trend was present in which there was a crescendo of abnormalities characterized by increased frequency of ventricular ectopic activity and ST-segment depression before the myocardial infarction and cardiac arrest. The authors proposed that had the information recorded by the ambulatory monitor been available to the attending staff, earlier treatment may have prevented cardiac arrest. Dodds and colleagues [7] reported a case in which a real time ambulatory ECG Holter monitor which was programmed to alarm when ischaemia was detected was used in a patient undergoing carotid artery surgery. In this case, detection of myocardial ischaemia occurred earlier, and consequently was treated earlier than would otherwise have been possible. Despite this the ischaemic episode progressed to myocardial infarction. However, the authors believed that relatively early recognition and treatment may have prevented further complications. Our patient was a high-risk cardiac case, with known phaeochromocytoma and previous myocardial infarction. The patient Was monitored with ambulatory arterial pressure monitoring and an ambulatory ECG monitor which was not programmed to alarm, but which requires downloading every 24 h. As a consequence, ST-segment depression indicating myocardial ischaemia was detected earlier than would otherwise have been the case. The additional use of ambulatory arterial pressure monitoring allowed us to observe that the development of myocardial ischaemia was associated with an increase in heart rate and arterial pressure compared with before operation when the patient had exhibited no signs of myocardial ischaemia. A 12-lead ECG was performed which confirmed the presence of ST-segment changes and the patient’s medication was altered in an effort to improve
494 haemodynamic control and reduce myocardial ischaemia, with an increase in atenolol dose and the commencement of oral nifedipine. Furthermore, staff were alerted to the patient’s condition. Despite this, the patient’s condition worsened and she developed symptoms of angina which required further medical treatment with GTN paste. However, the eventual outcome was good, and the patient did not progress to myocardial infarction. Several points are worthy of further comment. First, there are no previous reports of the use of ambulatory arterial pressure monitoring in the perioperative period. In this patient, we were able to identify that there was poor arterial pressure control after operation compared with before operation (using pressure recordings taken by the same monitor for a similar period), which in combination with an increased heart rate had resulted in myocardial ischaemia. Second, probably because the patient was initially asymptomatic, initial treatment was to increase the oral dose of -blocker and start a low oral dose of calcium antagonist. Had treatment been more aggressive at this stage, particularly with regard to improving heart rate and arterial pressure control with i.v. -block or GTN, myocardial ischaemia may have been controlled earlier, the development of angina prevented and the risk of progression to myocardial infarction further reduced. Indeed, even on the third postoperative day, heart rate and arterial pressure remained poorly controlled, and despite additional nitrate therapy, the patient continued to exhibit silent myocardial ischaemia. It was interesting that retrospective analysis of the data showed a significant association between heart rate and mean arterial pressure, and
British Journal of Anaesthesia both the duration and severity of myocardial ischaemia. Third, the monitors we use sound an alarm when ischaemia is detected, but for the purpose of our research this was disabled. Had the alarm facility been used, then myocardial ischaemia would have been detected at an earlier time.
Acknowledgement G. Troy is supported by a grant from Trent Health.
References 1. Mangano DT, Browner WS, Hollenberg M, London MJ, Tubau JF, Tateo IM. Association of perioperative myocardial ischaemia with cardiac morbidity and mortality in men undergoing noncardiac surgery. New England Journal of Medicine 1990; 323: 1781–1788. 2. Landesberg G, Luria MH, Cotev S, Eidelman LA, Anner H, Mossere M, Schechter D, Assaf J, Erel J, Berlatzky Y. Importance of long-duration postoperative ST-segment depression in cardiac morbidity after vascular surgery. Lancet 1993; 341: 715–719. 3. McHugh P, Gill NP, Wyld R, Nimmo WS, Reilly CS. Continuous ambulatory ECG monitoring in the perioperative period: Relationship of preoperative status and outcome. British Journal of Anaesthesia 1991; 66: 285–291. 4. O’Brien E, Mee F, Atkins N, O’Malley K. Accuracy of the Spacelabs 902207 determined by the British Hypertension Society protocol. Journal of Hypertension 1991; 9: 573–574. 5. Edwards ND, Reilly CS. Detection of perioperative myocardial ischaemia. British Journal of Anaesthesia 1994; 72: 104–115. 6. Clements FM, McCann RL, Levin RI. Continuous ST segment analysis for the detection of perioperative myocardial ischaemia. Critical Care Medicine 1986; 16: 710–711. 7. Dodds TM, Delphin E, Stone JG, Gal SG, Coromilas J. Detection of perioperative myocardial ischemia using Holter monitoring with real-time ST segment analysis. Anesthesia and Analgesia 1988; 67: 890–893.